1. Field of the Invention
This invention relates to a color information detecting device for use in detecting color temperature information, for example.
2. Description of the Prior Art
A conventional example of the circuit for detecting color temperature information is illustrated in FIG. 1, where a red (R) component and a blue (B) component are detected by respective sensors 1 and 2 positioned adjacent to each other. The outputs of the sensors 1 and 2 are amplified by amplifiers 3 and 5 while being logarithmically compressed by diodes 4 and 6 so that an R signal and a B signal of restricted dynamic range are obtained at the output of the amplifiers 3 and 5. These signals R and B are then applied to a subtractor composed of resistors R1 to R4 and an amplifier 7. As a result, their ratio is obtained.
Depending on this ratio of the R and B signals, either a value of color temperature to be displayed, or a gain control signal for the color image pickup device is read from the information in a memory unit such as a ROM.
This is based on the assumption that the ratio of the R and B signals varies as a single-valued function of the color temperature.
In such a conventional color temperature detecting device, however, because it uses two logarithmic compression circuits composed of the amplifiers 3 and 5 and the diodes 4 and 6, besides the increased complexity of structure, and since the temperature characteristics of the diodes 4 and 6 are not always the same, the information obtained at the output of the amplifier 7 is likely to be erroneous. To correct this error, the outputs of the amplifiers 3 and 5 must be connected to respective specified correction circuits. A problem encountered is that to achieve sufficient correction is difficult.
It is, therefore, an object of the present invention to provide a color information detecting device which has overcome the drawbacks of the prior art.
Another object is to provide a color information detecting device of simplified structure while permitting superior correction of the achieved temperature characteristic.